Comparative Study of Minimally Invasive Microwave Ablation Applicators

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors The authors propose a review of a number of simulation articles, by simulating again the systems proposed in literature. Although the list of references is exhaustive, I don't see any originality in the work. The paper tries to compare applicators from literature when simulated in the same conditions, but the conclusions should be more accurate. However, the introduction is well written. Fonts should be harmonized and a global english revision should be needed.

 

In my opinion, the contribution by the manuscript in terms of results (all the applicators are from literature and the simulations are repeated) is not sufficient for publication.

Author Response

Reviewer 1

 Comments

The authors propose a review of a number of simulation articles, by simulating again the systems proposed in literature. Although the list of references is exhaustive, I don't see any originality in the work. The paper tries to compare applicators from literature when simulated in the same conditions, but the conclusions should be more accurate. However, the introduction is well written. Fonts should be harmonized and a global english revision should be needed.

In my opinion, the contribution by the manuscript in terms of results (all the applicators are from literature and the simulations are repeated) is not sufficient for publication.

Author reply

We appreciate your thoughtful review and the time you took to evaluate our manuscript. Your feedback is highly valuable and helps us improve our work. We would like to address your concerns and clarify the purpose and contributions of our study. Initially, we need to clarify a misunderstanding, this article is considered to be a systematic review or comprehensive survey rather than a research paper aiming at a novel contribution.

 

• Contribution of the Work

Comment: The authors propose a review of a number of simulation articles, by simulating again the systems proposed in literature. Although the list of references is exhaustive, I don't see any originality in the work.

Author reply

The aim of our study was to provide a comparative analysis of microwave ablation antennas from the literature by simulating them under identical conditions. While it is true that the applicators are not novel, our work aims to fill a gap in the literature by ensuring an unbiased comparison using consistent parameters. This approach allows us to assess the performance of each antenna-applicator design on a fair basis, which has not been systematically done before.

A critical issue in microwave ablation refers to the restriction of the heated-ablated area inside the tumor, while protecting the surrounding healthy tissue. To avoid metastasis the established rule-of-thumb suggests the overheating of even a thickness of 1cm of the surrounding tissue, while maintaining the temperature increase in the healthy tissue beyond that less than 1⁰C. Obviously, a homogeneous model does not involve this information, since it models only the tumors. On the contrary, a two compartment model, one for the tumor and the other for healthy tissue provides the means to validate the applicators performance in this critical situation.

We believe that such a study provides a valuable reference for researchers and practitioners in the field, offering insights into how these designs perform under standardized conditions, which may aid in design improvements and clinical decision-making.

 

• Conclusions

Comment: The paper tries to compare applicators from literature when simulated in the same conditions, but the conclusions should be more accurate.

Author reply

We acknowledge your suggestion to make the conclusions more accurate. In the revised manuscript, we provided a deeper analysis of the results, highlighting specific trends.

Changes in the manuscript

Particularly, we added in conclusions section: This study presents the first comparative analysis of microwave ablation (MWA) applicators under standardized conditions, utilizing both homogeneous and two-compartment models. It also evaluates the safety aspects of MWA by investigating not only the temperature thresholds for effective treatment (50⁰C and 60⁰C) but also the isothermal contours at 42⁰C and 38⁰C. These contours are critical to ensuring the safety of MWA, a key factor in advancing this therapeutic modality. To achieve this, a two-compartment model, incorporating both tumor and healthy tissue, is employed. This model provides a robust framework for validating the performance of MWA applicators under these critical conditions.

 

• English Revision and Font Harmonization

Comment: Fonts should be harmonized and a global english revision should be needed.

Author reply

Thank you for pointing out these issues. We have carefully revised the manuscript to ensure consistency in fonts and to improve the language quality. We have also revised the manuscript professionally edited to address any remaining linguistic issues.

 

• Contribution of the Results

Comment: In my opinion, the contribution by the manuscript in terms of results (all the applicators are from literature and the simulations are repeated) is not sufficient for publication.

 Author reply

We understand your concern regarding the contribution of our results. We aim to demonstrate that our study is not just a repetition of past work but an effort to standardize evaluation conditions for comparative purposes. This could serve as a baseline for future designs and simulations in this domain. We made this contribution more explicit in the revised manuscript.

Changes in the manuscript

Explicitly, the following text was added in conclusions section: This study presents the first comparative analysis of microwave ablation (MWA) applicators under standardized conditions, utilizing both homogeneous and two-compartment models. It also evaluates the safety aspects of MWA by investigating not only the temperature thresholds for effective treatment (50⁰C and 60⁰C) but also the isothermal contours at 42⁰C and 38⁰C. These contours are critical to ensuring the safety of MWA, a key factor in advancing this therapeutic modality. To achieve this, a two-compartment model, incorporating both tumor and healthy tissue, is employed. This model provides a robust framework for validating the performance of MWA applicators under these critical conditions.

 

We hope that these revisions and clarifications address your concerns. Thank you once again for your constructive feedback and for recognizing the strengths of our introduction and reference list.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. In Table 2,  what parameters are represented by each letter in the column Values of parameters.

2. Fig.2. is a self-imitation of the figure, can not visualise the comparison with the original study of each figure.

3. When analysing the results of  Fig. 2, it is stated in line 182 that the shape of fig2 i) is close to a comet-tail shape, and in line 185 that the shape of fig2 i) is close to a spherical shape.

4. Section 3.2.2 analyses temperature diagrams, while the corresponding temperature diagram 4 is placed in subsection 3.2.1.

5. 279 line mentioned ‘ the homogeneous model are close to what depicted in the corresponding papers.’, the original paper is what, there is no comparison chart.

6. Why should the two-chamber model be simulated under the colon model when the homogeneous model is not the same set of data as he used.

8. 357 lines appeared Fig 8j and Fig 8j.

9. What software was used for the simulation and analysis, and what are the formulas for calculating the electromagnetic and thermal fields.

9. The title of 3.2.6 is the study under the same insertion depth and power, but the content analyses the effect of different power on the results.

10. The overall chapter arrangement of the article: results and discussion in section 3, discussion in section 4; whether subsections 3.1 and 2.3 overlap; whether the chapter arrangement in section 3 is reasonable.3.2 The title of 3.2 is the performance of all the designs in the homogeneous model, and the content of 3.2.3-3.2.5 in the later section is the analysis of performance in the two-chamber model. 3.2.6 shows the comparison results under two models (homogeneous model, two-chamber model).

Author Response

Reviewer 2

 

Comments:

1. In Table 2, what parameters are represented by each letter in the column Values of parameters.
2. Fig.2. is a self-imitation of the figure, cannot visualize the comparison with the original study of each figure.
3. When analyzing the results of  Fig. 2, it is stated in line 182 that the shape of fig2 i) is close to a comet-tail shape, and in line 185 that the shape of fig2 i) is close to a spherical shape.
4. Section 3.2.2 analyses temperature diagrams, while the corresponding temperature diagram 4 is placed in subsection 3.2.1.
5. 279 line mentioned ‘the homogeneous model are close to what depicted in the corresponding papers.’, the original paper is what, there is no comparison chart.
6. Why should the two-chamber model be simulated under the colon model when the homogeneous model is not the same set of data as he used.
7. 357 lines appeared Fig 8j and Fig 8j.
8. What software was used for the simulation and analysis, and what are the formulas for calculating the electromagnetic and thermal fields.
9. The title of 3.2.6 is the study under the same insertion depth and power, but the content analyses the effect of different power on the results.
10. The overall chapter arrangement of the article: results and discussion in section 3, discussion in section 4; whether subsections 3.1 and 2.3 overlap; whether the chapter arrangement in section 3 is reasonable.3.2 The title of 3.2 is the performance of all the designs in the homogeneous model, and the content of 3.2.3-3.2.5 in the later section is the analysis of performance in the two-chamber model. 3.2.6 shows the comparison results under two models (homogeneous model, two-chamber model).

 

Author reply

Thank you for your thorough review and detailed feedback on our manuscript. We greatly appreciate the time and effort you invested in providing such constructive comments. Below, we address each of your points:

 

• Parameters in Table 2

Comment: 1. In Table 2, what parameters are represented by each letter in the column Values of parameters.

 

Author reply

We regret the lack of clarity in the description of the parameters in Table 2. In the revised manuscript, we have included a detailed legend explaining what each letter represents in the column “Values of parameters.” This will ensure the table is self-explanatory and informative.

Changes in the manuscript

Specifically, the caption of table 2 was revised: Details on the Designs’ Parameter Values (All parameters listed in Table 2 correspond to magnitudes depicted in Figure 1 for the respective applicators).

 

• Figure 2 and Comparison with Original Studies

Comment: 2. Fig.2. is a self-imitation of the figure, cannot visualize the comparison with the original study of each figure.

 

Author reply

We acknowledge that Figure 2 does not adequately visualize the comparison with the original studies. To address this, we have revised Figure 2 to include side-by-side comparisons of our simulated results with the corresponding figures from the original studies. This will provide a clearer visual context for the reader and a scale bar of temperature next to each image.

Changes in the manuscript

An indicative example is as below: (figure is included in the attached file)

1. h) Balun-free based-fed monopole -> Figure 4,5 at [47]

 

• Inconsistencies in Shape Descriptions (Lines 182 & 185)

Comment: 3. When analyzing the results of  Fig. 2, it is stated in line 182 that the shape of fig2 i) is close to a comet-tail shape, and in line 185 that the shape of fig2 i) is close to a spherical shape.

Author reply

Thank you for pointing out the inconsistency in the description of Figure 2(i). We have revised the analysis and ensure consistent terminology is used throughout. When the shape varies under specific conditions, we have clearly explained these variations and provided justification for any observed differences.

Changes in the manuscript

Particularly, figure 2(i) was erased from line 185. The corresponding changes in the text are as follows:

The applicators in Figure 2 a), c), d), f), g) and i) retain the comet-tail shape of ablation area, which causes difficulties in ensuring the safe exposure of healthy tissues on the back side of the applicators. On the contrary, the treated area is closer to a spherical shape in Figure 2 b), h). However, it is only in Figure 2 j) that the ablation area is restricted inside the tapered spiral providing the means to control the exposure of the healthy tissue. 

 

• Placement of Temperature Diagrams (Section 3.2.2 and Figure 4)

Comment: 4. Section 3.2.2 analyses temperature diagrams, while the corresponding temperature diagram 4 is placed in subsection 3.2.1.

Author reply

We understand the confusion caused by the placement of Figure 4 in subsection 3.2.1 instead of 3.2.2. In the revised manuscript, we ensured that all figures are placed in the corresponding subsections to maintain logical consistency and improved readability.

 

• Original Paper Reference (Line 279)

Comment: 5. 279 line mentioned ‘the homogeneous model are close to what depicted in the corresponding papers.’, the original paper is what, there is no comparison chart.

Author reply

The statement in line 279 lacks sufficient clarity regarding which original paper is being referred to. In the revised manuscript, we have explicitly cited the original studies being compared and, where possible, included a comparison chart to highlight how our results align with theirs.

Changes in the manuscript

Specifically, the appropriate references were added are: As we can see from Fig. 4, the results of our simulations for the homogeneous model are close to what depicted in the corresponding papers [21,41 ,43-48].

 

• Two-Chamber Model Simulation and Data Sets

Comment: 6.Why should the two-chamber model be simulated under the colon model when the homogeneous model is not the same set of data as he used.

Author reply

We appreciate your question about the rationale for using the two-chamber model. In the revised manuscript, we provided a detailed justification for simulating the two-chamber model under the colon model, even when the homogeneous model is based on a different dataset. The rationale behind this is: A critical issue in microwave ablation refers to the restriction of the heated-ablated area inside the tumor, while detecting the surrounding healthy tissue. To avoid metastasis the established rule-of-thumb suggests the overheating of even a thickness of 1cm of the surrounding tissue, while maintaining the temperature increase in the healthy tissue beyond that less than 1⁰C. Obviously, a homogeneous model does not involve this information, since it models only the tumors. On the contrary, a two compartment model, one for the tumor and the other for healthy tissue provides the means to validate the applicators performance in this critical situation.

The tissue and tumor model in Section 3.2.3 is based on the work presented in Reference 41, which analyzed the helical open waveguide structure in the context of large intestine tissue. Our study extends this reference by providing a parametric analysis of the same antenna, specifically by varying the monopole length and spiral height to optimize its performance. To ensure consistency with the original study and facilitate meaningful comparisons, the large intestine model was retained for this specific analysis.

For all other sections, we employed a liver model to provide a unified comparison across various designs. This approach balances the need to extend prior work with the objective of creating a consistent evaluation framework. We have clarified this rationale in the revised manuscript for better understanding. We also explain further the dielectric properties of liver and tumor at liver giving the corresponding references too. This part is mentioned at section 3.3.

Changes in the manuscript

3. The following text is added in the manuscript at section 3.2:

The tissue and tumor model in this section is placed in the large intestine, consistent with [41], which initially analyzed the helical open waveguide structure under these conditions. This study extends the findings of [41] by performing a parametric analysis of the same antenna, varying the monopole length and spiral height to optimize its performance in the large intestine model. In contrast, for simulations in other sections we employed a liver model to provide a unified evaluation framework for comparing different designs. This approach ensures both consistency with prior studies and meaningful cross-design comparisons.

1. The following text is added in the manuscript at conclusions section:

This study presents the first comparative analysis of microwave ablation (MWA) applicators under standardized conditions, utilizing both homogeneous and two-compartment models. It also evaluates the safety aspects of MWA by investigating not only the temperature thresholds for effective treatment (50⁰C and 60⁰C) but also the isothermal contours at 42⁰C and 38⁰C. These contours are critical to ensuring the safety of MWA, a key factor in advancing this therapeutic modality. To achieve this, a two-compartment model, incorporating both tumor and healthy tissue, is employed. This model provides a robust framework for validating the performance of MWA applicators under these critical conditions.

 

• Repeated Mention of “Fig. 8j” (Line 357)

Comment:7. 357 lines appeared Fig 8j and Fig 8j.

Author reply

Thank you for pointing out the repeated mention of “Fig. 8j.” This was an oversight, and we have corrected it in the revised manuscript to ensure accurate references to all figures. Particularly, we replaced Fig. 8j with Fig. 8g.

Changes in the manuscript

Therefore, at the section 3.3.2, the text is: Fig. 8g and 8j show that the temperature contours above 42⁰C restricted inside or slightly outside the tumor boundary.

 

• Calculation Formulas

Comment: 8.What software was used for the simulation and analysis, and what are the formulas for calculating the electromagnetic and thermal fields.

Author reply

We have provided the formulas used for calculating electromagnetic and thermal fields to ensure transparency and reproducibility of our results in section 2.3 Simulation Framework and Methods for Applicator Analysis.

Changes in the manuscript

2.3 Simulation Framework and Methods for Applicator Analysis  (For a version including equations, please see the attached file)

Microwave ablation (MWA) involves the absorption of electromagnetic energy by biological tissues, leading to localized heating. The electromagnetic field distribution is governed by Maxwell's equations:

                                                                                                 (1)

                                                                                              (2)

where  and  are the electric and magnetic fields, ε is the electrical permittivity, μ is the magnetic permeability, ω is the angular frequency and  is the current density.

These equations are coupled with tissue dielectric properties to calculate the power deposition in tissues, quantified as Specific Absorption Rate (SAR) [50]:

                                                                                               (3)

where σ is the tissue conductivity,  is the electric field strength, and ρ is the tissue density. The resultant heat diffusion in the tissue is governed by the Penne’s bioheat equation:

                                                 (4)

where ρ and c​ are the tissue density and specific heat, T is the temperature, k is the thermal conductivity, Q represents the heat generated by electromagnetic absorption (SAR), the perfusion term accounts for cooling by blood flow  and  reflects tissue metabolism.  

In the electromagnetic simulations, boundary conditions of Perfectly Matched Layers (PML) are applied at the computational domain boundaries to absorb outgoing waves and prevent artificial reflections. For thermal boundary conditions, a constant temperature is assumed at the tissue surface, set to body temperature (37°C). This assumption simplifies the modeling while aligning with the study's focus on standardized comparisons across applicator designs.

These equations and conditions provide the foundation for accurate modeling of electromagnetic and thermal fields, enabling the standardized comparison of applicator designs in this study. By incorporating realistic material properties and boundary conditions, this approach ensures that simulation results are closely aligned with experimental and clinical scenarios. Herein, a commercial electromagnetic simulator (CST) is utilized which incorporates the above equations and reliably solves both the electromagnetic and thermal problems.

 

• Title and Content of Section 3.2.6

Comment: 9.The title of 3.2.6 is the study under the same insertion depth and power, but the content analyses the effect of different power on the results.

Author reply

We recognize the discrepancy between the title of Section 3.2.6 and its content. In the revised manuscript, we have aligned the section title with the content and restructured the section to focus solely on the stated topic (i.e., the effect of the same insertion depth and power).

Changes in the manuscript

Therefore, the new title is: 3.4 Quantitative comparison of ablation performance across applicators under standardized conditions

 

• Overall Chapter Arrangement and Overlaps

Comment: 10. The overall chapter arrangement of the article: results and discussion in section 3, discussion in section 4; whether subsections 3.1 and 2.3 overlap; whether the chapter arrangement in section 3 is reasonable.3.2 The title of 3.2 is the performance of all the designs in the homogeneous model, and the content of 3.2.3-3.2.5 in the later section is the analysis of performance in the two-chamber model. 3.2.6 shows the comparison results under two models (homogeneous model, two-chamber model).

Comment: The overall chapter arrangement of the article: results and discussion in section 3, discussion in section 4

Author reply

• Results and Discussion Sections: We have reviewed and revised the structure of sections 3 and 4 to avoid redundancy and ensure a clear and logical flow of information. Particularly section 3 is the results and section 4 the discussion.

Comment: whether subsections 3.1 and 2.3 overlap;

Author reply

• Overlaps between Subsections 3.1 and 2.3: We have carefully examined these sections to remove any unnecessary overlaps while preserving relevant information.

Changes in the manuscript

We integrated subsections 3.1 and 2.3 to subsection: 2.4 Verification of already existed designs

Comment: whether the chapter arrangement in section 3 is reasonable. 3.2 The title of 3.2 is the performance of all the designs in the homogeneous model, and the content of 3.2.3-3.2.5 in the later section is the analysis of performance in the two-chamber model. 3.2.6 shows the comparison results under two models (homogeneous model, two-chamber model).

Author reply

• Chapter Arrangement in Section 3: We agree that the chapter arrangement could be more coherent. We have restructured Section 3 to clearly separate the analysis of the homogeneous model, the two-chamber model, and their comparative analysis. Titles and content are revised accordingly to eliminate confusion.

Changes in the manuscript

Therefore, we revised the text and the new chapter arrangement is:

1. Introduction, 2. Materials and Methods, 2.1 Applicators structure: geometrical characteristics, 2.2 Comparison criteria, 2.3 Simulation Framework and Methods for Applicator Analysis, 2.4 Verification of already existed designs, 3 Results, 3.1 Performance in homogeneous model for all designs, 3.1.1 Specific Absorption Rate (SAR) for homogeneous model for all designs, 3.1.2 Temperature distribution for homogeneous model for all designs, 3.2 Temperature distribution of helical open waveguide structure vs. monopole for two-compartment model, 3.3 Performance in two-compartment model for all designs, 3.3.1 Specific Absorption Rate (SAR) for two-compartment model for all designs, 3.4 Quantitative comparison of ablation performance across applicators under standardized conditions, 4 Discussion, 5 Conclusions, References

 

Once again, we sincerely thank you for your insightful comments and suggestions. We are confident that these revisions will significantly improve the quality and clarity of our manuscript.

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article is clear and well written. This referee believes that it will be useful to researchers in the field of computational modeling. In particular, the correct quantification of the SAR plays a fundamental hole in the success of hyperthermia treatments.

 The article is recommended for publication after the following minor revision corrections:

i) Not only the parameters but also expressions regarding the Specific Absorption Rate (SAR) must be inserted in the text for completeness.

ii) In all tables it appears “Figure xx” at the last column.

Author Response

Reviewer 3

 

Comments:

The article is clear and well written. This referee believes that it will be useful to researchers in the field of computational modeling. In particular, the correct quantification of the SAR plays a fundamental hole in the success of hyperthermia treatments.

The article is recommended for publication after the following minor revision corrections:

1. i) Not only the parameters but also expressions regarding the Specific Absorption Rate (SAR) must be inserted in the text for completeness.
2. ii) In all tables it appears “Figure xx” at the last column.

 

Author reply

Thank you very much for your positive feedback and for recommending our manuscript for publication after minor revisions. We appreciate your acknowledgment of the article’s clarity and potential usefulness to researchers in the field. Below, we address your suggestions in detail:

• Specific Absorption Rate (SAR) Expressions

Comment: i) Not only the parameters but also expressions regarding the Specific Absorption Rate (SAR) must be inserted in the text for completeness.

Author reply

We agree that including expressions related to the Specific Absorption Rate (SAR) will enhance the completeness of the text. In the revised manuscript, we have incorporated the relevant SAR equations and provided a brief explanation of their significance in computational modeling and hyperthermia treatments. This addition will ensure that readers can fully understand the context and application of SAR in our study.

Changes in the manuscript

This part is the section 2.3 Simulation Framework and Methods for Applicator Analysis. The changes read as:

 

2.3 Simulation Framework and Methods for Applicator Analysis (For a version including equations, please see the attached file)

Microwave ablation (MWA) involves the absorption of electromagnetic energy by biological tissues, leading to localized heating. The electromagnetic field distribution is governed by Maxwell's equations:

                                                                                                 (1)

                                                                                              (2)

where  and  are the electric and magnetic fields, ε is the electrical permittivity, μ is the magnetic permeability, ω is the angular frequency and  is the current density.

These equations are coupled with tissue dielectric properties to calculate the power deposition in tissues, quantified as Specific Absorption Rate (SAR) [50]:

                                                                                               (3)

where σ is the tissue conductivity,  is the electric field strength, and ρ is the tissue density. The resultant heat diffusion in the tissue is governed by the Penne’s bioheat equation:

                                                 (4)

where ρ and c​ are the tissue density and specific heat, T is the temperature, k is the thermal conductivity, Q represents the heat generated by electromagnetic absorption (SAR), the perfusion term accounts for cooling by blood flow  and  reflects tissue metabolism.  

In the electromagnetic simulations, boundary conditions of Perfectly Matched Layers (PML) are applied at the computational domain boundaries to absorb outgoing waves and prevent artificial reflections. For thermal boundary conditions, a constant temperature is assumed at the tissue surface, set to body temperature (37°C). This assumption simplifies the modeling while aligning with the study's focus on standardized comparisons across applicator designs.

These equations and conditions provide the foundation for accurate modeling of electromagnetic and thermal fields, enabling the standardized comparison of applicator designs in this study. By incorporating realistic material properties and boundary conditions, this approach ensures that simulation results are closely aligned with experimental and clinical scenarios. Herein, a commercial electromagnetic simulator (CST) is utilized which incorporates the above equations and reliably solves both the electromagnetic and thermal problems.

 

• “Figure xx” in Tables

Comment: ii) In all tables it appears “Figure xx” at the last column.

 

Author reply

Thank you for highlighting this formatting issue. We have revised all tables in the manuscript and replace “Figure xx” with the correct figure references. This will ensure that the tables are clear and consistent with the rest of the text.

 

We are grateful for your constructive comments and the opportunity to improve our manuscript.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

In this article, the author studied the design of different types of optical fibers for microwave ablation. In the title, the author wrote, minimally invasive, but the implantation of optical fiber requires surgery which is an invasive procedure. Apart from that, there are several other comments listed below:

1. The manuscript didn't have a section detailing the simulation or methods used to generate the simulation results displayed through the manuscript.

2. In figure 1, when the author displays different designs, there is no scale bar illustrating the geometrical size of the structures. This comment also applies to all the figures showing simulation results and the size of the heating area is unknown without scale bars.

3. All designs of different optical fibers are taken from existing publications, which put the novelty and significance of this manuscript questionable.

Author Response

Reviewer 4

 

Comments:

In this article, the author studied the design of different types of optical fibers for microwave ablation. In the title, the author wrote, minimally invasive, but the implantation of optical fiber requires surgery which is an invasive procedure. Apart from that, there are several other comments listed below:

1. The manuscript didn't have a section detailing the simulation or methods used to generate the simulation results displayed through the manuscript.
2. In figure 1, when the author displays different designs, there is no scale bar illustrating the geometrical size of the structures. This comment also applies to all the figures showing simulation results and the size of the heating area is unknown without scale bars.
3. All designs of different optical fibers are taken from existing publications, which put the novelty and significance of this manuscript questionable.

Author reply

Thank you for your detailed review and for pointing out several areas where our manuscript could be clarified or improved. We value your input and are grateful for the opportunity to respond to your concerns. Below, we address each of your points:

• Title and the Use of "Minimally Invasive"

Comment: In this article, the author studied the design of different types of optical fibers for microwave ablation. In the title, the author wrote, minimally invasive, but the implantation of optical fiber requires surgery which is an invasive procedure.

Author reply

We understand your concern regarding the use of the term "minimally invasive" in the title. While the term refers to the general nature of microwave ablation procedures that typically involve minimal surgical intervention compared to open surgery, we have clarified this distinction in the introduction. This addresses any potential misunderstanding regarding the invasiveness of the technique.

Changes in the manuscript

The corresponding text reads:

Introduction

Microwave ablation (MWA) has emerged as a prominent thermal therapy technique for the treatment of tumors. As a minimally invasive procedure, it offers a promising alternative to traditional surgical methods, providing the benefits of reduced recovery time, lower risk of complications and side effects and the potential for outpatient treatment. Therefore, MWA is a powerful tool in the fight against cancer, a disease that has plagued humanity from its emergence and is one of the leading causes of death worldwide. The primary mechanism of MWA involves the use of microwave energy to generate heat, inducing localized coagulative necrosis of tumor cells. This procedure has been effectively applied to a range of cancers, including liver, lung, kidney, bone tumors etc, making it a versatile tool in the oncological arsenal [1-5].

The efficacy and safety of microwave tumor ablation heavily depends on the design and performance of the microwave applicator and the device responsible for delivering microwave energy to the targeted tissue [6].

 

• Methods Section for Simulations

Comment: 1. The manuscript didn't have a section detailing the simulation or methods used to generate the simulation results displayed through the manuscript.

Author reply

Thank you for highlighting the absence of a detailed methods section. In the revised manuscript, we have included a dedicated section detailing the simulation process and the specific parameters employed. This addition enhanced the transparency and reproducibility of our work.

Changes in the manuscript

This section is 2.3 Simulation Framework and Methods for Applicator Analysis. The added text reads:

2.3 Simulation Framework and Methods for Applicator Analysis (For a version including equations, please see the attached file)

Microwave ablation (MWA) involves the absorption of electromagnetic energy by biological tissues, leading to localized heating. The electromagnetic field distribution is governed by Maxwell's equations:

                                                                                                 (1)

                                                                                              (2)

where  and  are the electric and magnetic fields, ε is the electrical permittivity, μ is the magnetic permeability, ω is the angular frequency and  is the current density.

These equations are coupled with tissue dielectric properties to calculate the power deposition in tissues, quantified as Specific Absorption Rate (SAR) [50]:

                                                                                               (3)

where σ is the tissue conductivity,  is the electric field strength, and ρ is the tissue density. The resultant heat diffusion in the tissue is governed by the Penne’s bioheat equation:

                                                 (4)

where ρ and c​ are the tissue density and specific heat, T is the temperature, k is the thermal conductivity, Q represents the heat generated by electromagnetic absorption (SAR), the perfusion term accounts for cooling by blood flow  and  reflects tissue metabolism.  

In the electromagnetic simulations, boundary conditions of Perfectly Matched Layers (PML) are applied at the computational domain boundaries to absorb outgoing waves and prevent artificial reflections. For thermal boundary conditions, a constant temperature is assumed at the tissue surface, set to body temperature (37°C). This assumption simplifies the modeling while aligning with the study's focus on standardized comparisons across applicator designs.

These equations and conditions provide the foundation for accurate modeling of electromagnetic and thermal fields, enabling the standardized comparison of applicator designs in this study. By incorporating realistic material properties and boundary conditions, this approach ensures that simulation results are closely aligned with experimental and clinical scenarios. Herein, a commercial electromagnetic simulator (CST) is utilized which incorporates the above equations and reliably solves both the electromagnetic and thermal problems.

 

• Scale Bars in Figures

Comment: 2. In figure 1, when the author displays different designs, there is no scale bar illustrating the geometrical size of the structures. This comment also applies to all the figures showing simulation results and the size of the heating area is unknown without scale bars.

Author reply

We appreciate your observation regarding the lack of scale bars in Figure 1 and other figures displaying simulation results. In the revised manuscript, we added scale bars to all relevant figures. Particularly, we added scale bars next to each image in figure 2. Also, we explain that magnitudes mentioned at table 2 with their units representing the magnitudes in figure 1. This will provide readers with a clear understanding of the geometrical sizes and dimensions involved.

Changes in the manuscript

An indicative example is as below: (figure is included in the attached file)

1. h) Balun-free based-fed monopole -> Figure 4,5 at [47]

As aware the magnitudes, the caption of table 2 was revised: Details on the Designs’ Parameter Values (All parameters listed in Table 2 correspond to magnitudes depicted in Figure 1 for the respective applicators).

 

• Clarification on Optical Fibers

Comment: 3. All designs of different optical fibers are taken from existing publications,

Author reply

We believe there may have been a misunderstanding regarding the content of our study. Our manuscript focuses on comparing microwave ablation applicators, as indicated by the title, "Comparative Study of Minimally Invasive Microwave Ablation Applicators." Optical fibers are not part of the scope of this work. To avoid any confusion, we have carefully reviewed the text to ensure that the focus remains clear and consistent throughout the manuscript.

 

• Novelty and Significance of the Work

Comment: which put the novelty and significance of this manuscript questionable.

Author reply

A critical issue in microwave ablation refers to the restriction of the heated-ablated area inside the tumor, while protecting the surrounding healthy tissue. To avoid metastasis the established rule-of-thumb suggests the overheating of even a thickness of 1cm of the surrounding tissue, while maintaining the temperature increase in the healthy tissue beyond that less than 1⁰C. Obviously, a homogeneous model does not involve this information, since it models only the tumors. On the contrary, a two compartment model, one for the tumor and the other for healthy tissue provides the means to validate the applicators performance in this critical situation.

While it is true that all designs studied are based on existing publications, the primary objective of our work is to provide a comparative analysis of these designs under standardized conditions. This approach offers an unbiased assessment of their performance, which has not been systematically documented in the literature.

 

Changes in the manuscript

The following text is added in the manuscript at conclusions section: This study presents the first comparative analysis of microwave ablation (MWA) applicators under standardized conditions, utilizing both homogeneous and two-compartment models. It also evaluates the safety aspects of MWA by investigating not only the temperature thresholds for effective treatment (50⁰C and 60⁰C) but also the isothermal contours at 42⁰C and 38⁰C. These contours are critical to ensuring the safety of MWA, a key factor in advancing this therapeutic modality. To achieve this, a two-compartment model, incorporating both tumor and healthy tissue, is employed. This model provides a robust framework for validating the performance of MWA applicators under these critical conditions.

 

We are confident that these revisions will address your concerns and improve the quality and clarity of our manuscript. Thank you again for your constructive comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The new version clarifies the review purpose of the proposed manuscript. The authors addressed clearly all the points requested by the reviewer.

Reviewer 4 Report

Comments and Suggestions for Authors

Thanks for responding to my previous comments and the authors have addressed my concerns.